<!DOCTYPE html>  
<meta charset="utf-8" />  
<title>async</title>  
<body>
    <h2>async</h2>  
</body>
<script type="text/javascript">
    const delay = timeout => new Promise(resolve=> setTimeout(resolve, timeout));
    const sleep =async ()=>{
        await delay(1000);
        return 'aa'
    }
    sleep().then((data)=>{
        console.log('data',data)
    })

</script>
</html>